Pressure-induced disappearance of the local rhombohedral distortion in BaTiO3.

BaTiO has been studied by X-ray absorption spectroscopy at the Ti K edge up to 19GPa in a diamond anvil cell at room temperature. The pre-edge features observed at the Ti K edge are sensitive to the pressure. It is shown that the high-pressure cubic phase obtained above 2GPa is similar to the high-temperature one, with titanium out of the centre of the oxygen octahedron. Between 2 and 10GPa the intensity of the pre-edge features decreases indicating that the Ti atom is moving toward the centre of the oxygen octahedron. Above 10GPa, the features do not change anymore, showing that the Ti atom is at the centre of the oxygen octahedron. No correlation between the Ti atom position and the Raman activity under pressure is observed